Technical Schematics for the BCM, do they exist?

[spleenharvester]

I believe I have shorted one of the DRL drivers on my 2011 312's BCM by incorrectly wiring a new DRL socket. The 21W filament is now as dim as the 5W filament and pops up a "Check daytime running lights" message on the dash, and the BCM logs these codes:

• B1022-12 - Left or front side lights short circuit to +V
• B1033-18 - Daylights current too low

I have some board level repair experience (albeit in computers not automotive) so I want to take a look at the BCM board. The problem is I cannot find what part of the board is responsible for driving the DRLs. Does anyone have any kind of schematic, the only information I can find relates to cloning?

Also what are the risks of pulling the BCM, does it object to being unplugged in any way provided the battery is unplugged?

Thank you

 

[spleenharvester]

Following up on this now that I have the BCM in hand - the DRLs are driven by a BTS5241G in SOIC-20 package in the far corner on my board, though it looks like some revisions have a similar chip in SOP-12 package. BCM was an absolute pig to remove from its casing but we got there. On my car it was held in by those bolts that are designed to have their head shear off when tightened, but I was able to loosen them with vice grips so no drilling needed. I couldn't find anything obvious wrong with the BTS5241G circuit with the board powered off, so I removed the chip and reinstalled in the car for time being and cleared errors - both the short circuit to +V and daylights current too low errors have disappeared and have been replaced by a daylights current too high error (which is what you expect when the pin is left floating - obviously the DRLs do not fire in this scenario!).

I can also confirm that (a) at least on my car, this package only seems to drive the DRLs through the OUT1 channel and nothing else - OUT2 pins do go to a single pin on the header but on my car there is no corresponding wire on the loom - possibly fog lights as my car doesn't have those?; and (b) removing the BCU hasn't screwed anything up, all my keys still work fine etc, though obviously make sure you unplug the battery first.

Have attached the datasheet for BTS5241G. I think the most likely explanation is that I have damaged the gate on OUT1. If I am correct then hopefully replacing this BTS5241G should fix the problem. I've ordered a cheap donor BCM in the hopes it will have the correct chip as these are out of production and not easy to get hold of. I'll update if it fixes it.

Also steps to remove the BCM on this car (right hand drive) since all the tutorials seem to be for left hand drive and the Haynes manual doesn't even bother:

1. Disconnect negative terminal of battery
2. Empty out glove box and remove plastic cover at back - this covers the fuses on the BCM, and a big long allen bolt holding the glove box in place
3. Remove the big long allen bolt
4. There are four (torx/allen?) bolts holding the top of the glove box in place - two on the top left, one on the top right, and one in the middle behind that flap that folds down - remove them all
5. Remove the two (torx/allen?) bolts at the bottom corners of the glove box. Glove box should now pull out
6. BCM is now exposed. Loosen two headless bolts at the top of the metal cage cover and one at the bottom of the metal cage cover using vice grips, then you should be able to twist them off with your fingers and remove the cover
7. Unplug the front harnesses - minimal force should be required to disengage the plastic clips!
8. Push in two plastic tabs at the left and at the right hand side of the metal cage, and slide the BCM backwards slightly
9. Disengage the two rear harnesses from the BCM (this is a bit fiddly)
10. Rotate the BCM bottom facing towards you - you should be able to slide it out of the cage through the front

I won't give steps on how to remove the casing because it is just a god damn nightmare of clips, see this video:

 

[spleenharvester]

Replaced the DRL smart switch IC (BTS5241G) and the sidelight IC (BTS5234G), fault persists. To confirm:

-DRL 21W filament lights dimly with headlights both on and off
-With DRLs on and headlights off with codes cleared, there are no errors
-If I then turn the headlights on the BCM immediately logs

• B1022-12 - Left or front side lights short circuit to +V
• B1033-18 - Daylights current too low

Any ideas? I've tried comparing various regions to the donor board and I cannot find any differences. I'm struggling to think of anything that would impact both the DRL and the side lights this way.

 

[spleenharvester]

Okay I've resigned this repair, I think the fault is probably somewhere between the two PCBs and I think I will just knacker it worse trying to separate the push pins, which I obviously don't want to risk when I'm going to get it cloned.

I've ordered a replacement BCM to clone onto, if I plug it in before the cloning does anyone know if the DRLs should switch on?

 

[puntodad19]

Interesting...I can only assume you have checked all related earth's, as you know bad earth's can and do cause all sorts of wierd electrical issues.....

 

[spleenharvester]

Interesting...I can only assume you have checked all related earth's, as you know bad earth's can and do cause all sorts of wierd electrical issues.....

Yeah it's deffo the BCM, it happened right after the reverse polarity incident and I spent the whole night farting about with it, don't know what else it could be at this point